mirror of
https://git.postgresql.org/git/postgresql.git
synced 2024-08-23 21:07:19 +02:00
Rewrite comments in replication slot advance implementation
The code added by 9c7d06d606
was a bit obscure; clarify that by
rewriting the comments. Lack of clarity has already caused bugs, so
it's a worthy goal.
Co-authored-by: Arseny Sher <a.sher@postgrespro.ru>
Co-authored-by: Michaël Paquier <michael@paquier.xyz>
Co-authored-by: Álvaro Herrera <alvherre@alvh.no-ip.org>
Reviewed-by: Petr Jelínek <petr.jelinek@2ndquadrant.com>
Discussion: https://postgr.es/m/87y3fgoyrn.fsf@ars-thinkpad
This commit is contained in:
parent
dc961e5822
commit
96bd49437c
@ -338,7 +338,10 @@ CreateInitDecodingContext(char *plugin,
|
||||
* that, see below).
|
||||
*
|
||||
* output_plugin_options
|
||||
* contains options passed to the output plugin.
|
||||
* options passed to the output plugin.
|
||||
*
|
||||
* fast_forward
|
||||
* bypass the generation of logical changes.
|
||||
*
|
||||
* read_page, prepare_write, do_write, update_progress
|
||||
* callbacks that have to be filled to perform the use-case dependent,
|
||||
|
@ -317,10 +317,11 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
|
||||
}
|
||||
|
||||
/*
|
||||
* Helper function for advancing physical replication slot forward.
|
||||
* The LSN position to move to is compared simply to the slot's
|
||||
* restart_lsn, knowing that any position older than that would be
|
||||
* removed by successive checkpoints.
|
||||
* Helper function for advancing our physical replication slot forward.
|
||||
*
|
||||
* The LSN position to move to is compared simply to the slot's restart_lsn,
|
||||
* knowing that any position older than that would be removed by successive
|
||||
* checkpoints.
|
||||
*/
|
||||
static XLogRecPtr
|
||||
pg_physical_replication_slot_advance(XLogRecPtr moveto)
|
||||
@ -340,68 +341,89 @@ pg_physical_replication_slot_advance(XLogRecPtr moveto)
|
||||
}
|
||||
|
||||
/*
|
||||
* Helper function for advancing logical replication slot forward.
|
||||
* Helper function for advancing our logical replication slot forward.
|
||||
*
|
||||
* The slot's restart_lsn is used as start point for reading records,
|
||||
* while confirmed_lsn is used as base point for the decoding context.
|
||||
* The LSN position to move to is checked by doing a per-record scan and
|
||||
* logical decoding which makes sure that confirmed_lsn is updated to a
|
||||
* LSN which allows the future slot consumer to get consistent logical
|
||||
* changes.
|
||||
*
|
||||
* We cannot just do LogicalConfirmReceivedLocation to update confirmed_flush,
|
||||
* because we need to digest WAL to advance restart_lsn allowing to recycle
|
||||
* WAL and removal of old catalog tuples. As decoding is done in fast_forward
|
||||
* mode, no changes are generated anyway.
|
||||
*/
|
||||
static XLogRecPtr
|
||||
pg_logical_replication_slot_advance(XLogRecPtr moveto)
|
||||
{
|
||||
LogicalDecodingContext *ctx;
|
||||
ResourceOwner old_resowner = CurrentResourceOwner;
|
||||
XLogRecPtr startlsn = MyReplicationSlot->data.restart_lsn;
|
||||
XLogRecPtr retlsn = MyReplicationSlot->data.confirmed_flush;
|
||||
XLogRecPtr startlsn;
|
||||
XLogRecPtr retlsn;
|
||||
|
||||
PG_TRY();
|
||||
{
|
||||
/* restart at slot's confirmed_flush */
|
||||
/*
|
||||
* Create our decoding context in fast_forward mode, passing start_lsn
|
||||
* as InvalidXLogRecPtr, so that we start processing from my slot's
|
||||
* confirmed_flush.
|
||||
*/
|
||||
ctx = CreateDecodingContext(InvalidXLogRecPtr,
|
||||
NIL,
|
||||
true,
|
||||
true, /* fast_forward */
|
||||
logical_read_local_xlog_page,
|
||||
NULL, NULL, NULL);
|
||||
|
||||
CurrentResourceOwner = ResourceOwnerCreate(CurrentResourceOwner,
|
||||
"logical decoding");
|
||||
/*
|
||||
* Start reading at the slot's restart_lsn, which we know to point to
|
||||
* a valid record.
|
||||
*/
|
||||
startlsn = MyReplicationSlot->data.restart_lsn;
|
||||
|
||||
/* Initialize our return value in case we don't do anything */
|
||||
retlsn = MyReplicationSlot->data.confirmed_flush;
|
||||
|
||||
/* invalidate non-timetravel entries */
|
||||
InvalidateSystemCaches();
|
||||
|
||||
/* Decode until we run out of records */
|
||||
while ((startlsn != InvalidXLogRecPtr && startlsn < moveto) ||
|
||||
(ctx->reader->EndRecPtr != InvalidXLogRecPtr && ctx->reader->EndRecPtr < moveto))
|
||||
/* Decode at least one record, until we run out of records */
|
||||
while ((!XLogRecPtrIsInvalid(startlsn) &&
|
||||
startlsn < moveto) ||
|
||||
(!XLogRecPtrIsInvalid(ctx->reader->EndRecPtr) &&
|
||||
ctx->reader->EndRecPtr < moveto))
|
||||
{
|
||||
XLogRecord *record;
|
||||
char *errm = NULL;
|
||||
XLogRecord *record;
|
||||
|
||||
/*
|
||||
* Read records. No changes are generated in fast_forward mode,
|
||||
* but snapbuilder/slot statuses are updated properly.
|
||||
*/
|
||||
record = XLogReadRecord(ctx->reader, startlsn, &errm);
|
||||
if (errm)
|
||||
elog(ERROR, "%s", errm);
|
||||
|
||||
/*
|
||||
* Now that we've set up the xlog reader state, subsequent calls
|
||||
* pass InvalidXLogRecPtr to say "continue from last record"
|
||||
*/
|
||||
/* Read sequentially from now on */
|
||||
startlsn = InvalidXLogRecPtr;
|
||||
|
||||
/*
|
||||
* The {begin_txn,change,commit_txn}_wrapper callbacks above will
|
||||
* store the description into our tuplestore.
|
||||
* Process the record. Storage-level changes are ignored in
|
||||
* fast_forward mode, but other modules (such as snapbuilder)
|
||||
* might still have critical updates to do.
|
||||
*/
|
||||
if (record != NULL)
|
||||
if (record)
|
||||
LogicalDecodingProcessRecord(ctx, ctx->reader);
|
||||
|
||||
/* Stop once the moving point wanted by caller has been reached */
|
||||
/* Stop once the requested target has been reached */
|
||||
if (moveto <= ctx->reader->EndRecPtr)
|
||||
break;
|
||||
|
||||
CHECK_FOR_INTERRUPTS();
|
||||
}
|
||||
|
||||
/*
|
||||
* Logical decoding could have clobbered CurrentResourceOwner during
|
||||
* transaction management, so restore the executor's value. (This is
|
||||
* a kluge, but it's not worth cleaning up right now.)
|
||||
*/
|
||||
CurrentResourceOwner = old_resowner;
|
||||
|
||||
if (ctx->reader->EndRecPtr != InvalidXLogRecPtr)
|
||||
@ -409,7 +431,7 @@ pg_logical_replication_slot_advance(XLogRecPtr moveto)
|
||||
LogicalConfirmReceivedLocation(moveto);
|
||||
|
||||
/*
|
||||
* If only the confirmed_flush_lsn has changed the slot won't get
|
||||
* If only the confirmed_flush LSN has changed the slot won't get
|
||||
* marked as dirty by the above. Callers on the walsender
|
||||
* interface are expected to keep track of their own progress and
|
||||
* don't need it written out. But SQL-interface users cannot
|
||||
|
Loading…
Reference in New Issue
Block a user